Water control system using oxidation reduction potential sensing

ABSTRACT

An automatic control system for maintaining the quality of water in a cooling tower utilizes a probe (38) which senses the oxygen reduction potential (ORP) of a soap having a 1:1 stoichiometric equivalent of mineral acid and ammonia or amine in the water. The soap is pumped from a chemical supply means (20) containing the soap in response to the ORP of the soap in the water falling below a predetermined threshold. A second sensing probe measures the conductivity (in MHos) of the water as a factor of the total dissolved solids (TDS) to control the bleed-off or blow-down of the water. The chemicals, which are supplied for maintaining the ORP, permit significantly higher total dissolved solids in the water than with standard cooling tower systems, without the buildup of scale. As a consequence, water consumption is significantly reduced; and the system functions automatically, without requiring periodic visual inspection, water analysis or manual operation.

RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.059,514 filed May 17, 1993, now U.S. Pat. No. 5,268,092, which is acontinuation of application Ser. No. 829,762 filed on Feb. 3, 1992, nowabandoned, both assigned to the same assignee as the presentapplication. Also related is application Ser. No. 700,780, filed May 16,1991, and the disclosure of that application is incorporated herein byreference. This application is also related to application Ser. No.08/099,738, filed Jul. 30, 1993.

BACKGROUND

Water cooling towers are in widespread use for large capacity heatexchange systems. These cooling towers are used to remove absorbed heatfrom a circulating water coolant by evaporating a portion of the coolantin the cooling tower. The remaining coolant is extracted from areservoir or sump at the base of the tower by a pump, and suppliedthrough the heat load on a continuous basis. Because a large quantity ofwater evaporates in such a system, a significant and fairly rapidbuild-up of scale, sludge and the like takes place in the water. Variouschemicals are employed preventing the precipitation out of the mineralsin the water, since such precipitation causes what is known as "scaling"on the surfaces of the cooling tower and heat exchange equipment. Ifsuch scaling is not prevented or is not periodically removed, it canresult in significantly reduced heat transfer, and, therefore,significantly increased operating costs. In addition, it enhancescorrosion of the heat exchange surfaces beneath the scale.

In addition to the scaling problem mentioned above, if the pH factor inthe water is too low (typically, below 6.8), increased corrosion of thesystem components can result. If the pH is too high, the significantscale build-up mentioned above, takes place. Consequently, it has beenthe practice to add chemicals to the cooling tower water to maintain abalanced or "safe" range of pH factor in the coolant.

Even with the addition of chemical additives to maintain a chemicalbalance in the coolant water, the constant significant evaporation of aportion of the water rapidly builds up the amount of total dissolvedsolids (TDS) in the water to the point where scaling can occur, eventhough scale-retardant chemicals are present in the water. To preventscaling from occurring, it is customary periodically to remove waterwith a high TDS content from the system to reduce the TDS, or toincrease the oxidizing potential or pH. When water is removed, it isreplaced with "make-up" water, which typically is obtained from thelocal available or modified water supply. The removal or dumping ofwater from the system is accomplished in one or the other of two ways,namely a "bleed-off" in which a portion of the sump or reservoir wateris drained while the system is operating, or by "blow-down", whichtypically is a complete draining of the sump. In both cases, the waterwhich is drained off is replaced with the "make-up" water.

Typically, the dumping of water by either "bleed-off" or "blow-down" incooling tower systems, is effected when the TDS is somewhere around5,000 ppm. In most systems, a TDS in excess of 5,000 ppm results inscaling, even with the use of chemical additives and oxidants.

In the past, the decision to initiate dumping of water from thereservoir of the cooling tower generally has been manually determined.In some cases, such dumping simply is done on a periodic basis. In othercases, a visual inspection of the water in the cooling tower is made todetermine whether or not to effect dumping of some of that water. Thisis a very imprecise technique, and typically results in the dumping ofexcessive quantities of water from the system.

A system, which has been developed for providing a somewhat more precisecontrol of the dumping or bleed-off of water from a cooling towersystem, is disclosed in the patent to O'Leary U.S. Pat. No. 4,464,315.This patent includes probes for sensing the conductivity of the coolingtower water, as well as the conductivity of the make-up water. Theprobes provide signals to a controller unit, which proportionallyadjusts the trip point at which dumping of the cooling tower wateroccurs, based upon the sensed water conductivities. A problem with asystem of the type disclosed in the O'Leary patent, however, is that atTDS concentrations of 5,000 ppm or less, the differences in conductivityat different TDS concentrations are relatively small; so that accuratedetermination of the concentration required for dumping of water isdifficult. In addition, for such low TDS concentrations, frequentdumping, either by way of blow-down or bleed-off, is required, resultingin the waste of substantial quantity of water.

The water which is dumped from a cooling tower system represents asignificant loss. In a typical, relatively small and relativelyefficient evaporative cooling tower system, a total amount ofapproximately 637,000 gallons per year of water is consumed by thecooling tower. 0f this amount, 437,000 gallons are evaporated in thecooling process. The other 200,000 gallons is flushed down the sewer inthe bleed-off operation. This ratio, of approximately one-third of thetotal amount of water used being totally wasted, is typical of suchsystems. Some cooling tower systems waste an even greater quantity ofwater. Not only does this wasted water result in an appreciable loss,both in the resource of the water itself, and in its cost; but mostcooling tower systems use chemicals or additives, such as acids,anti-fouling agents and corrosion inhibitors, to prevent corrosion andscaling from occurring. These chemicals constitute a substantialenvironmental risk, since in many cases the chemicals are toxic and/orhazardous.

The patent to Derham U.S. Pat. No. 4,931,187 discloses another coolingtower system in an effort to automate control of pH, temperature andTDS. In the Derham system, these parameters are monitored to control theaddition of make-up water to the cooling tower, either by means of abypass or through a water softener, or both, in accordance with thedifferent variables measured by the system. Derham states that thesystem eliminates virtually any bleed-off of coolant. To accomplishthis, however, an additional particle filter must be included to removesuspended solids from the coolant. It is necessary, however, to backwashthe filter with water from outside the system on a periodic basis. It isnot clear how scaling can be prevented without any dumping of the waterrecirculated in the cooling tower system, since at some point the TDS inthat water reaches a saturation point. While some precipitated solidswill be removed by the filter 20, it appears that scaling also can occuras a result of saturation, irrespective of the operation of the watersoftener and the filter. These additional components also require extraperiodic maintenance for their operation.

Other cooling tower systems have been designed, which include anautomatic pre-established timer control of backwash and chemicaladdition (Derham U.S. Pat. No. 3,628,663) or some type of floatresponsive to the water level in the cooling tower for controllingeither make-up water addition (Kinkead U.S. Pat. No. 4,836,239), ormake-up water addition and chemical addition (O'Leary U.S. Pat. No.3,788,340 and Glad No. 3,627,032).

In addition to corrosion and scaling conditions, materials areintroduced through air, water and environmental changes, which providesources for biological support of aerobic or anaerobic algae and thelike. While, to some extent, suspended solids in the water may provide avisual indication of the existence of undesirable biological conditions,typically, the conditions are not discernable to the viewer until acritical condition exists.

It is desirable to provide automatic control of the electron equilibriumof the water in a system, to significantly reduce the amount of waterwhich must be dumped from the system, to accurately sense the conditionsrequired for the addition of chemical additives, with a minimum ofmaintenance or supervision in its operation.

SUMMARY OF THE INVENTION

This invention is directed to an automatic control system adapted forcontrolling scale formation in a water circulating system, comprising:

first sensing means for measuring the oxygen reduction potential (ORP)of the circulating water containing a soap having a 1:1 stoichiometricequivalent of a mineral acid and a base selected from the groupconsisting of an amine and ammonia in the water for controlling scaleformation in said system and supply means for automatically supplyingsaid soap in response to a predetermined ORP measured by said firstsensing means substantially corresponding to a pH higher or lower than aselected range for controlling said scale.

In the above-identified applications Ser. Nos. 829,762 and 059,514, asoap of a mineral acid and a base selected from the group consisting ofan amine and ammonia has been disclosed as an additive for controllingscale in circulating water employing an automatic control system bymeasuring the oxygen reduction potential (ORP) of the water containingthe soap and supplying soap upon demand. It has now been found thatsoaps of a mineral acid and a base selected from the group consisting ofan amine and ammonia can also be employed in the automatic controlsystem. The mineral acids are selected from group consisting ofhydrochloric acid, sulfuric acid and nitric acid.

It is an object of this invention to provide an improved water system.

It is an additional object of this invention to provide an improvedautomatic control of the operation of a water system.

It is another object of this invention to provide an improved controlsystem for a water system for automatically monitoring the conditionsrequired for adding chemical additives to the water, and effecting theaddition of such additives to control various parameters affecting thewater quality.

It is a further object of this invention to provide an improved watersystem for effectively controlling the dumping of water from the systemin response to the conductivity of the water, and for automaticallyadding chemical additives to the water in response to a sensed conditionof the water.

In accordance with a preferred embodiment of the invention, an automaticcontrol system for a water system includes a first sensor (ORP sensor)for measuring the oxygen reduction potential (REDOX) of the waterrecirculated in the water system. A reservoir for the soap of a mineralacid and a base such an amine or ammonia is coupled with the ORP sensorto supply the soap to the water whenever a pre-established ORP ismeasured by the ORP sensor. Another sensor measures the conductivity ofthe water, as a factor of total dissolved solids (TDS). Whenever theconductivity (measured in mHos) of the cooling tower water(representative of TDS) reaches a pre-established conductivity, water isremoved or dumped from the system.

BRIEF DESCRIPTION OF THE DRAWING

The sole figure of the drawing is a diagrammatic representation of apreferred embodiment of the invention.

DETAILED DESCRIPTION

Before entering into a description of the operation of the system shownin the drawing, a brief discussion of ORP measurement is in order. ORPis a measurement of the electron exchange potential which occurs in anionic reaction, Since most heat transfer systems, including coolingtower systems, are constructed of metal, utilizing ever-changing water,there typically is an undesired equilibrium created. The ORP measurementallows control of the electrochemical equilibrium. Chemical equilibriadetermines whether the stable form of a material is soluble orinsoluble. If soluble species of material are stable, it is possible fora metal rapidly to corrode into aqueous forms. If insoluble species ofmaterial are stable, there is a tendency to form a scale, inhibitingcorrosion, but inducing "under scale" corrosion. Both corrosion andscale are undesirable conditions in a cooling tower system, sincedegradation of the system operation occurs when either of theseconditions are present to any substantial extent.

Two terms commonly used in chemistry and important to note from thestandpoint of corrosion are oxidation and reduction. Oxidation may bedifficult to pinpoint, since according to corrosion terminology, it canmean either the rusting of iron or the development of white oxides onaluminum or zinc. In order to understand their meanings from a chemicalstandpoint, it is necessary to examine a chemical formula such as thatfor iron: ##STR1##

This formula indicates iron in water in a state of equilibrium where nocurrent flow exists. The "Fe" is iron as a metal, the "Fe⁺⁺ " is theionized form of iron, and the electrons indicate the negative chargesgiven up when the metal changes to an ion. The movement of the iron fromthe metal form to the ion form is called oxidation. Therefore, in acorrosion cell, the metal is oxidized when it goes into solution as anion. This occurs at the anode where the term oxidation also commonlyapplies to rust forms.

When proceeding in the opposite direction and adding electrons to theionized iron, the reaction occurs in the direction of the iron as metal,and is referred to as reduction. A metal, therefore, which has beenchanged from its oxidized state to the metal, has been reduced. This iswhat takes place when iron ore is changed to metal in a blast furnace.

Different metals have different capacities for being reduced and forbeing oxidized. Gold, for example, exists primarily in the reducedstate, e.g., as a metal. Potassium, on the other hand, exists primarilyin either the oxidized state as an oxide or in the ionic state as asalt. The symbolic reaction for iron given above and its relativepotential for the electrochemical reactions known is called anoxidation-reduction potential. It may also be called a redox potential,half-cell potential, or solution potential.

The benefit of ORP measurement is that when it is calculated properly,it permits maintenance of a system such as a cooling tower system,within operable, ideal parameters. in the operation of the preferredembodiment described subsequently, it has been found that to controlcorrosion or scaling, the oxidation potential must be controlled. Theoxidation electrochemical reaction produces an electron flow which canbe measured through ORP measurement probes. This measured potential thenmay be utilized to effect the introduction of controlled quantities ofadditives to control corrosion or scale, regardless of changingenvironmental conditions. ORP measurements also are affected by othervariables, including biological; so that the analysis of changingenvironmental factors can be controlled through ORP instrumentation.This is accomplished by the system disclosed in the drawing.

Reference now should be made to the drawing, which illustrates apreferred embodiment of the invention. The embodiment shown in FIG. 1functions to permit up to 30,000 ppm TDS concentration (measured as 0 to100,000 mHos) in the water recirculated in a cooling tower systemwithout scale or corrosion. This is accomplished by the use of chemicaladditives of the type disclosed in the above identified co-pendingapplications which are incorporated herein by reference, to control thequality of the water. These additives of the present inventionpreferably comprise aqueous solutions of 1:1 stoichiometric soaps of amineral acid, such as hydrochloric, sulfuric and nitric acid, and a basesuch as an amine or ammonia. These soaps are effective in solubilizingmagnesium and calcium carbonate, which are predominate constituents ofwater scale/deposit. The concentration levels of the chemical additivesare measured by measuring the ORP (oxygen reduction potential) of thewater containing the additives.

A conventional cooling tower 10 is shown. The cooling tower 10 has asump or reservoir 11 at its bottom, with a pipe 12 for introducingmake-up water whenever the water level in the sump 11 drops below someminimum level. A pump 15 withdraws the water from the reservoir 11through a pipe or conduit 14, and supplies that water through anotherpipe or conduit 17 to a heat load 18, from which the water continuesthrough the pipe 17 to spray nozzles 19 located in the top of thecooling tower 10. The system described thus far is a conventionalcooling tower system, and may be constructed in a variety of differentstandard configurations.

In the system shown in the drawing, a reservoir 20 for a liquid chemicaladditive is indicated, with a pump 21 located to withdraw chemicals fromthe reservoir 20 through a pipe 22, and supply those chemicals through apipe 24 and an injection T 25 and a T 26 to the water recirculatingthrough the conduit or pipe 17. In systems of the prior art, the pump 21typically would be operated in response to a manually activated controlat such times and for such durations as determined by an observer of thewater quality recirculating through the system.

In the system disclosed in the drawing, however, control of the pump 21is effected through a meter/monitoring unit 40. The inputs to themonitoring unit 40 are provided from an ORP probe 38, a pH probe 37 anda conductivity probe 36 located in a measuring section 34 of a shuntline connected between a T 27 and the T 26. A valve 28 is locatedbetween the T 27 and a strainer 29 to supply water in the shunt througha flow regulator 30 to establish a constant flow rate; so that themeasurements made by the probes 36, 37 and 38 are constant, irrespectiveof changing flow conditions which may take place in the conduit 17. Atthe outlet side of the unit 34 is another valve 39. The valves 28 and 39typically are manually controlled valves, which are normally open; sothat the shunt is constantly operated to bypass small amount of thewater supplied from the pump 15 through the shunt for the measurement bythe probes 36, 37 and 38. All of the water which passes through thesection 34 is returned to the recirculating water in the system by meansof the T 26.

The probe 38 is a standard ORP probe (such as TBI model 540)manufactured by TBI-Baily controls), and it supplies ORP voltage orpotential measurements to the ORP monitoring/comparison section 44 inthe unit 40. The measured potentials typically are characterized asoxidation potentials, since the magnitude of the measured potential fromthe probe 38 is representative of the relative ease with whichreductants in the water oxidize. It has been found that measurement ofORP provides a more accurate indication of the condition of the waterthan a measurement of pH, since pH is difficult to adjust in a system ofthe type shown in the drawing in which the water has very high TDS. Asmentioned above, an ideal composition for the additive in the reservoir20, for effecting the removal and prevention of scale in the coolingtower water, has been found to be a composition containing a 1:1stoichiometric equivalent of a mineral acid and amine or ammoniaaccording to this invention. Various minerals acids and ammonia or anamine may be used in accordance with this invention.

Whenever a condition is sensed by the ORP probe 38, indicative thatadditional chemical additives need to be supplied to the recirculatingwater in the system, the comparison section 44 operates an ORP outputswitch 50 to provide a signal to a pump 21 to operate the pump towithdraw additive through the pipe 22 from the reservoir 20. Thisoperation continues until the ORP potential measured by the probe 38returns to a "safety" range of potential. At that time, the ORP switch50 is once again opened, and the pump 21 ceases operation.

The pH probe 37 is optional, but may be used in addition to the ORPprobe 38 to control the addition of acid to the water from a reservoir65. If low acidic conditions are sensed by the probe 37, a signal issupplied to a monitoring/comparison section 45 in the unit 50. Thesection 45 operates a pH switch 49 to provide a signal to a pump 66. Thepump 66 withdraws acid from the reservoir 65 and supplies it through apipe 67 to a T 69, where the acid is added to the recirculating water inthe system. This operation continues until the pH sensed by the probe 37is correct. The switch 49 then is opened, and the pump 66 is turned off.

When the chemical additive contains a 1:1 stoichiometric soapequivalent, as described above, applicant has found that the TDS (totaldissolved solids) in the water, which can be reached without scaling orcorrosion, are significantly higher than the 5,000 ppm typical ofconventional cooling tower systems. TDS concentrations of 30,000 ppm ,or higher, (measured as 0 to 100,000 mHos) can be attained by the systemwithout requiring dumping by way of either bleed-off or blow-down of thewater from the cooling tower reservoir. Consequently, the conductivitysensor 36 coupled to the unit 40 is set to measure conductivity producedby these significantly higher TDS levels. Since the TDS level of thewater can be an order of magnitude or more than can be tolerated inconventional systems a much more sensitive or accurate conductivityprobe 36 may be employed. Whenever the TDS level reaches a level of forexample 30,000 ppm, a signal is provided by the conductivity probe 36 tothe comparison section 46 to cause a conductivity switch 52 to beclosed. This supplies a signal to operate a solenoid-controlled valve 54located in a bleed-off shunt from the conduit 17. The bleed-off iseffected through a normally open manual valve 56 and a strainer 57 todump the bleed-off or blow-down water from the reservoir 11 of thecooling tower. The strainer 57 is provided to prevent silt and otherparticles from interfering with the proper operation of the valve 54.

The operation of the conductivity switch 52 may be effected until theconductivity sensed by the probe 36 drops to some second lowerpredetermined value, whereupon the switch 52 is opened to turn off thevalve 54. This is a typical operation for a "bleed-off" dumping of waterfrom the system while it is continuously running. Obviously, make-upwater through the pipe 12 will be provided to the sump 11, as soon asthe water level drops to some minimum value, as described above, as aresult of the dumping of water through the valve 54.

Operation of the switch 52 may be used to coordinate the operation ofthe valve 54 with a sensor or float in the reservoir and another valve(not shown) between the water supply and the pipe 12 illustrated in thedrawing. In this condition, all of the water in the sump could bedumped, if desired, (blow-down). After this has been accomplished, asmeasured by the float in the reservoir 11, the valve 54 is once againclosed, and make-up water is permitted to be supplied to the sump 11through the pipe 12.

Whenever there is a bleed-off or a blow-down of water from the reservoir11, an initial significant imbalance of the chemical condition of thewater occurs as a result of replacement of a substantial quantity (orreplacement of all) of the water in the cooling tower system.Consequently, an additional solenoid-controlled valve 59 and a biocidalfeeder 60 also preferably are provided to biologically shock the systemsimultaneously with the operation of the blow-down or bleed valve 54.The valve 59 is operated by the switch 52 with the valve 54.

The additives, described above, as supplied from the reservoir 20, arenot affected when the chemicals in the biocidal feeder are quaternaryammonia compounds. Thus, if such compounds are provided in the biocidalfeeder 60, these compounds are mixed with water, which is divertedthrough the valve 59 from a T 61 to a T 63 to be added to the watercirculating through the conduit 17. Quaternary ammonia is a nonoxidizingbiocide for use in microbial suppression and destruction.

Oxidizing compounds, however, also can be supplied by the biocidalfeeder 60 to obtain the desired microbial treatment. A typical preferredoxidizing compound contains bromine. Bromine compounds cause the ORPreadings to increase significantly. This condition, however, istemporary, and normal operation of the ORP sensing and control resumeswithin a relatively short time after each "shock" treatment from thefeeder 60.

The drawing also illustrates devices which may be coupled to themeter/monitor 40 for providing a record of the observed conditionsestablished by the probes 36 and 38. For example, the signals which arecontinuously produced by the probes 36 and 38 may be supplied to acomputer system 70 for processing, to a modem 71 for transmission to aremote location, or to a printer or plotter 73 to provide a continuousrecord of the conductivity and ORP being monitored. In addition, analarm 74 may be provided to produce a visible or audible indicationwhenever either of the probes 36 and 38 provide an output indicative ofan out-of-balance condition of the water recirculating through thecooling tower 10. These devices 70, 71, 73 and 74 are not necessary forthe automatic operation of the system which has been described, but maybe utilized in conjunction with that system to enhance its utility bymonitoring its operation.

An additional valve 76 has been illustrated connected between the valve28 and 29 in the shunt line to permit a sample of the water to bewithdrawn from the system for test purposes. Normally, the valve 76 isclosed; and water is only withdrawn infrequently for conducting analysisof the water quality which is not covered by the automatic systemdescribed above.

What has been discovered, is that ORP parameters, if set up correctly inthe comparator or meter 44, analyze the solubility of the water with amillivolt reading output from the probe 38. Any element in the water,irrespective of its characteristics, affects the ORP. If the ORP readingraises, the solubility of the water increases. If the ORP readinglowers, the solubility decreases.

ORP is an electron activity measurement. This measurement is related tothe pH of the water, and by maintaining the ORP within a safety range,currently arbitrarily independently calibrated at the set-up of eachsystem operation, the pH remains between 6.8 and 8.5. Consequently, aslong as the ORP is set, the only considerations which remain to be dealtwith in the system are microbial corresponding to silt accumulation,biological activity and specific gravity. The table below illustratesthe relationship between ORP readings (in millivolts) and pH, along witha designation of the cooling tower water conditions which producecorrosion and scaling.

                  TABLE 1                                                         ______________________________________                                        pH                     ORP (millivolts)                                       ______________________________________                                        14        SCALING      -1000                                                  8.5                     -100                                                  7         SAFETY ZONE     0                                                   6.8       CORRODING     +100                                                  0                       1000                                                  ______________________________________                                    

The ORP reading which correspond to pH of 6.8 and 8.5, respectively,initially must be independently calibrated for each system. It has beenfound that even when the same make-up water 12 is supplied to twoidentical systems side-by-side, ORP readings may vary considerably.Consequently, as the sump water concentrates with solids, ORP readingsneed to be determined which correspond with the pH readings ofsignificance (typically, 6.8 and 8.5). Once these have been established,the comparator in the ORP meter 44 is adjusted accordingly to respond tothese readings. The readings then remain consistent throughout theoperation of the system; and fully automatic cooling tower systemoperation is possible. An ideal starting water condition is given below:

    ______________________________________                                        CONDITION         MIN      MAX                                                ______________________________________                                        TEMPERATURE        40° F.                                                                          80° F.                                     pH                 6.8       7.4                                              OXIDANT FREE & TOTAL                                                                             0.0       1.5    mg/L                                      TOTAL ALKALINITY   60       180     mg/L                                      TOTAL DISSOLVED SOLIDS                                                                          500      1750     ppm                                       CONDUCTIVITY      750      2625     mHos                                      TOTAL HARDNESS    100       300     mg/L                                      CALCIUM HARDNESS  150      1000     mg/L                                      DISSOLVED OXYGEN   6        10      mg/L                                      ______________________________________                                    

The system which has been described above typically reduces the waterdumped from the system, whether the water is dumped by means ofbleed-off or blow-down, by as much as 95% over conventional coolingtower systems. This is equivalent to a 30% reduction in the total waterconsumption for the process. As a result, significant savings inoperating costs are realized. In addition, utilization of the chemicaladditives described above significantly reduces the fouling of thecooling tower system; so that more efficient operation takes place, andlonger life of all of the system components results. This equates toadditional significant savings.

1:1 SOAP CHEMICAL CONSTITUENT STUDIES

1. COOLING TOWER CHEMISTRY CONSIDERATIONS

Cooling towers are normally scaled and feed water also contains "basic"chemicals such as calcium and magnesium carbonates, bicarbonates,hydroxides, etc. In the chemistry studied there is (1) free hydroxaceticacid (HOAcOH) which gives the compositions a pH of about 3, (2) a 1:1soap or quaternary ammonium compound between triethanolamine (TEA) andhydroxacetic acid, i.e. [TEAH]+[OAcOH]-, where the hydrogen ion orproton has transferred from the hydroxacetic acid the free electron pairon the nitrogen and (3) sodium xylene sulfonate (SXS). When thecomposition is added to cooling towers, the excess hydroxyacetic acidpresent reacts rapidly with the scale and/or calcium and magnesiumcompounds, etc. in solution to form the corresponding calcium,magnesium, etc. soaps which are much more soluble than the scale andinorganic carbonates, etc. The operating of pH range of the coolingtower continues in the range of 9 to 6.5 because the free hydroxyaceticacid has been consumed.

According to the above identified applications, the 1:1 soap is thereaction product of a weak organic acid and a weak amine base whichinherently is in equilibrium with low levels of free hydroxyacetic acidand triethanolamine. This equilibrium allows for free hydroxyacetic acidto be generated, even under basic conditions, which in turn can reactwith inorganic carbonates, etc. for continued protection of the toweragainst scale formation.

2. ORP STUDIES ON CHEMICAL SPECIES

In the ORP studies that follow, it was of interest to determine theeffect on ORP readings for hydroxyacetic acid, triethanolamine, sodiumxylene sulfonate, the hydroxyacetic ion and the 1:1 neutral soap betweentriethanolamine and hydroxyacetic acid. The results of these studieswere conducted in "conditioned" tap water (i.e., boiled and stirreduntil ORP leveled off).

HYDROXYACETIC ACID

The results indicate that hydroxyacetic acid has the greatest effect onORP increasing it some 220 units when present in over 0.04% wt.Hydroxyacetic acid, as such, would not be present in an operatingcooling tower since it is rapidly consumed by reaction with the scale,etc. present.

1:1 SOAP OF TRIETHANOLAMINE AND HYDROXYACETIC ACID

The lowest level of 0.01% wt. for the 1:1 soap gave an increase in theORP of about 30 units and remained essentially constant with increasingconcentration up to 0.20% wt. This indicates that low levels of the 1:1soap can be detected by ORP.

It is important to determine if the ORP is detecting thetriethanolammonium ion, [TEAH]+, or the hydroxyacetic ion, [OAcOH]-,particularly in the pH range of 9 to 6.5 for cooling tower operation.

SODIUM HYDROXYACETATE

A neutral solution of sodium hydroxy acetate was prepared and added tothe ORP test solution. The ORP essentially did not change with theaddition of sodium hydroxyacetate. The presence of the hydroxyacetateion does not effect the ORP reading. Also, it is well known that thesodium ion does not have an effect on ORP.

The increase in ORP for this 1:1 soap is therefore attributed to thetriethanolammonium ion, [TEAH]+. This ionic species can exist in the pHrange of 9 to 6.5 in cooling towers. As long as it's presence can bedetected there will be hydroxyacetic acid available via the equilibriumdiscussed above, which can then control the scale forming tendencies inthe system. When it can no longer be detected, the ORP meter will callfor additional soap.

SODIUM XYLENE SULFONATE

Sodium xylene sulfonate, the reaction product of a strong acid and astrong base, has no effect on ORP when added up to 0.20% wt. in thisstudy.

TRIETHANOLAMINE

The addition of triethanolamine, which is 85% triethanolamine and 15%diethanolamine, decreases the ORP reading somewhat with increase inconcentration. In earlier work, TEA was found to be very low inconductivity in aqueous solutions. Although TEA is a weak base, it willincrease the pH of an aqueous solution to about 9 by reacting with waterto form low levels of hydroxide ion. It was earlier demonstrated thatORP is very sensitive to changes in pH in the range of pH=9 to 6. Forthis reason it was not unexpected that TEA would decrease the ORPslightly in this test.

OTHER 1:1 SOAPS

Several other neutral soaps of weak organic acids with triethanolaminewere prepared and added to conditioned tap water to determine the effecton ORP. The results are summarized in Table A.

                  TABLE A                                                         ______________________________________                                        ACID           ORP INCREASE                                                   ______________________________________                                        Hydroxyacetic  30                                                             Acetic         28                                                             Citric         26                                                             Benzoic        27                                                             ______________________________________                                    

It appears that the 1:1 soaps of weak acids and weak bases (amines)result in essentially the same increase in ORP. This is expected as thesame triethanolammonium ion, [TEAH]+, is present in all the soapstested. Other amines include morpholine imidazole, 3-picoline anddiethylamine.

TITRATION CURVE STUDIES OF A 1:1 SOAP OF A MINERAL ACID AND AMMONIA ORAMINE

A new experiment was designed to further simulate cooling towerapplications of the chemistry. Ammonia or an amine was added to aboutone liter of conditioned tap water (or acidified conditioned tap wateras noted) with vigorous stirring. An ORP reading was then taken whenstabilized.

Mineral acids were then added in small increments with vigorousstirring. The experiments were modeled after thetriethanolamine/hydroxyacetic acid soaps and employed the same relativeequivalents so that the curves can be compared on a nearly equivalentbasis. The ORP of the solution was measured over a period of 5 to 15min. after the addition and an average ORP taken as the plot point.During the addition of the acid the corresponding "ammonium" ion isformed by reaction of the acid with ammonia or amine which increases theORP measurement.

The following titration curve studies were conducted:

1. 1:1 SOAP OF AMMONIA AND HYDROCHLORIC ACID

Acidified conditioned tap water was employed. Upon addition of ammoniathe ORP decreased 107 units and the solution was clear with a pH of 9.Upon incremental addition of hydrochloric acid the ORP increasedessentially linearly over the basic pH range and then rapidly increasedand leveled over the acidic pH range. This indicates the ORP respondslinearly to the ammonia ammonium ion (soap) as it is formed.

2. 1:1 SOAP OF AMMONIA AND SULFURIC ACID

The procedure of Example 1 was repeated except that sulfuric acid wassubstituted for hydrochloric acid and the results were essentially thesame, namely, that the ORP responds linearly to the ammonium ion (soap)as it is formed.

3. 1:1 SOAP OF AMMONIA AND NITRIC ACID

The procedure of Example 1 was repeated except that nitric acid wassubstituted for hydrochloric acid and the results were essentially thesame, namely, that the ORP responds linearly to the ammonium ion (soap)as it is formed.

4. 1:1 SOAP OF THRIETHANOLAMINE AND HYDROCHLORIC ACID

The procedure of Example 1 was repeated except that thriethanolamine wassubstituted for ammonia and the results were essentially the same,namely, that the ORP responds linearly to the ammonium ion (soap) as itis formed.

5. 1:1 SOAP OF THRIETHANOLAMINE WITH SULFURIC ACID

The procedure of Example 4 was repeated except that sulfuric acid wassubstituted for hydrochloric acid and the results were essentially thesame, namely, that the ORP responds linearly to the ammonium ion (soap)as it is formed.

6. 1:1 SOAP OF THRIETHANOLAMINE WITH NITRIC ACID

The procedure of Example 4 was repeated except that nitric acid wassubstituted for hydrochloric acid and the results were essentially thesame, namely, that the ORP responds linearly to the ammonium ion (soap)as it is formed.

The foregoing description of the preferred embodiment of the inventionshould be considered as illustrative, and not as limiting. For example,although the embodiment described is used with a cooling tower, thesystem also may be used for water purification systems (distillation),reverse osmosis, etc., closed heat exchange systems (automotiveradiators), swimming pools, water distribution systems, and industrialsystems. Various other uses, changes and modifications will occur tothose skilled in the art, without departing from the true scope of theinvention as defined in the appended claims.

What is claimed is:
 1. An automatic control system adapted forcontrolling scale formation in a water circulating systemcomprising:first sensing means for measuring the oxygen reductionpotential (ORP) of the circulating water, the water containing a soaphaving a 1:1 stoichiometric equivalent of a mineral acid and a baseselected from the group consisting of an amine and ammonia forcontrolling scale formation in said system and supply means forautomatically supplying said soap in response to a predetermined ORPmeasured by said first sensing means substantially corresponding to a pHhigher or lower than a selected range for controlling said scale.
 2. Thesystem according to claim 1 further including:second sensing means formeasuring the conductivity of the water as a factor of total dissolvedsolids (TDS) in the water and means coupled with said second sensingmeans for removing water in response to the measurement of apredetermined conductivity of the water by said second sensing means. 3.The system according to claim 1 wherein the water is recirculated by apump through a recirculating conduit, and said first sensing meanssenses the soap in water supplied through the conduit by the pump. 4.The system according to claim 3 further including:a shunt conduitcoupled across at least a portion of the recirculating conduit so thatsaid first sensing means senses the soap in water flowing through saidshunt conduit.
 5. The system according to claim 1 wherein said soap insaid supply means is in liquid form, and further including a pump forremoving said soap from said supply means to supply said soap to saidwater, said pump being coupled with said first sensing means andoperated in response to the sensing of the predetermined ORP measured bysaid first sensing means.
 6. The system according to claim 2 whereinsaid means for removing water removes a predetermined quantity of waterfrom the system in response to the measurement of a predeterminedconductivity of such water by said second sensing means.
 7. The systemaccording to claim 2 wherein said means for removing water includes anormally-closed drain valve means; andmeans for opening saidnormally-closed drain valve means for a predetermined time interval inresponse to the measurement of said predetermined conductivity of thewater by said second sensing means.
 8. The system according to claim 7further including biocidal feeder means being coupled with said secondsensing means for supplying biocidal chemicals to said water in responseto the measurement of said predetermined conductivity of said water bysaid second sensing means.
 9. The system according to claim 1 whereinsaid soap in said supply means is in liquid form, and further includinga pump for removing soap from said supply means and for supplying saidsoap to said water, said pump coupled with said first sensing means andoperated in response to the sensing of a predetermined ORP measured bysaid first sensing means.
 10. The system according to claim 1 whereinthe mineral acid is selected from the group consisting of hydrochloricacid, sulfuric acid, and nitric acid and mixtures thereof.
 11. Thesystem according to claim 1 wherein the base selected is an amineselected from the group consisting of triethanolamine, morpholine,imidazole, 3-picoline and diethylamine, and mixtures thereof.